Defibrillators are implanted in patients susceptible to cardiac arrhythmias or fibrillation. Such devices provide cardioversion or defibrillation by delivering a high voltage shock to the patient's heart, typically about 500-750V. High voltage capacitors are used in defibrillators to accumulate the high voltage charge following detection of a tachyarrhythmia. It is desirable to make implantable devices as small as possible, with slim, flat packages being desired for pectorally implanted defibrillators. Therefore, flat capacitors have been developed to avoid the disadvantages of traditional cylindrical aluminum electrolytic capacitors.
Such a flat capacitor is disclosed in U.S. Pat. No. 5,522,851 to Fayram, which is incorporated herein by reference. Flat capacitors include a plurality of layers laminarly arranged in a stack. Each layer includes an anode and a cathode, with the anodes and cathodes being commonly connected to respective connectors. The layers may be cut in nearly any shape, to fit within a similarly shaped housing designed for a particular application. The capacitance of such a device is proportional to the number of layers, and to the area of each layer, providing significant design flexibility. However, it is desirable to further improve the capacitance per unit volume ratio of current devices, which currently devote some volume to clearances for preventing shorting of components, and to fastening and alignment elements for securing the device components to each other.
In addition, the process of manufacturing such capacitors is very labor intensive. The layer by layer assembly requires great care by the assembler to avoid damaging or misaligning any of the layers. The registration holes used in some devices aid manufacturing efficiency, but decrease the capacitance per unit volume and thus, the stored energy per unit volume.
The present invention overcomes the limitations of the prior art by providing a method of manufacturing an implantable cardiac defibrillator by forming a set of conductive sheets with the same profile having a sacrificial portion. An alignment figure is formed in each sheet, and the sheets are stacked and aligned by registering the alignment figures with each other. The sacrificial portions are removed from each of the sheets, which are secured together and positioned in a capacitor housing. Each sheet may include two major portions joined by the sacrificial portion, so that each major portion may become part of a separate capacitor stack after the sacrificial portion is removed, doubling manufacturing throughput.